Process for the production of N-methyl pyrrolidone using gamma butyrolactone and mixed methylamines as starting materials

ABSTRACT

A process for the production of N-methyl pyrrolidone using gamma butyrolactone and mixed methylamines as starting materials, in a continuous process, in such operating conditions as to allow the production of high purity N-methyl pyrrolidone in high yields.

BACKGROUND

The present invention relates to the production of N-methyl pyrrolidone(NMP). In particular, it relates to the use of gamma-butyrolactone (GBL)and mixed methylamines as starting materials, in such a way that theproduct is obtained by a continuous process in optimal purity andyields.

It is known from the prior art that there exist several processes forthe synthesis of N-methyl pyrrolidone, using GBL and one methylamine,monomethylamine (MMA), as starting materials.

In J. Am. Chem. Soc., March 1949, pag. 897, Elvain and Vozza described asynthetic strategy aimed at the production of NMP with GBL and MMA asstarting materials that exploited a discontinuous process, and with adouble amount of the latter in comparison with his stoichiometric value.

After 4 hours of reaction at 280° C., NMP was recovered by distillationwith a 90–93% yield.

In 1936 Spath and Lunder (Berichte 69, pag. 2727) described a similarprocess wherein a large excess of methylamine (4 mols per mol of GBL)was fed to a discontinuous reactor, with an approximately 90% conversionafter 3 hours.

JP-A-72/018751 discloses a discontinuous process for the preparation ofNMP by heating GBL with DMA and TMA. The reaction temperature is230–300° C. The reaction time is in the range of about 0 to 5 hours.After terminating the reaction, the separation of NMP can be performedby subjecting the reaction mixture to fractional distillation.

NMP product purification involved complex dissolution processes, to becarried out in the ether from the effluent of the reaction and theensuing distillations. In several patents (JD 7 221 420; JP 740025,G; JP7 420 585; JP 7 642 107) Mitsubishi Chemical Industries Co. Ltd. ofJapan described continuous processes for the synthesis of NMP using GBLand MMA as starting materials. These are characterised by reactions withhigh molar ratios between water and GBL (typically ranging between 3 and4 mols of water for each mol of GBL) and by the presence of greatamounts of MMA (typically with molar ratios ranging between 1.4 and 3mols of MMA per mol of GBL).

JP-A-01/190 667 teaches the preparation of NMP at 240–265° C. byreacting GBL with MMA, isolating the by-products DMA and TMA from theobtained reaction mixture and recirculating these by-products into thereaction system.

The processes designed by Mitsubishi result to be disadvantageous interms of the high costs involved with the separation of unreacted MMAand its recovery and with the separation of the water forwarded to thereaction to which synthesis water adds up (one mol of water for each molof reacted GBL).

To avoid the drawbacks associated with the discontinuous reaction in thepresence of excess MMA and water, alternative methodologies have beenproposed and these are based on the employment of catalysts. In GermanPatent No. 2,159,858 owned by Mobil Oil a synthesis with GBL, MMA in thepresence of 13X type zeolites is described.

The above processes did not succeed in being applied industrially, asthe employment of a catalyst subject to regenerations is disadvantageousin terms of the economic balance of the process as compared with noncatalytic processes.

In WO-A-99/52867 the same Applicant discloses a process for theproduction of N-Methyl Pyrrolidone by reacting in a continuous mode alight excess of pure monomethylamine with gamma-butyrolactone underpressure and without catalyst by using a three stage reactor connectedin series.

The present application is an improved low cost process to affordN-Methyl Pyrolidone by reacting gamma-butyrolactone with a mixture ofmethylamines.

The advantage of this application is the direct link established betweena N-Methyl Pyrrolidone plant and a Methylamines plant for a cheaperdesign. It is known that reacting ammonia and methyl over an aminationcatalyst produces a mixture of mono-, di- and trimethylamines. Theseparation of this mixture involves a complex separation sequence whichincreases significantly the price of pure methyl amines.

So, it is a first advantage of the present application to offer aprocess in which a low cost mixture of methylamines (coming directlyfrom the ammonia-methanol reaction without a costly fractionaldistillation step) is used to produce N-Methyl Pyrrolidone.

There is a second advantage of the present application. It is known inthe prior art that reacting separately gammabutyrolactone with mono-,di- and trimethylamines produces N-Methyl Pyrrolidone with water and,for the two last amines, water and methanol.

According to the present invention, by using the process disclosed inWO-A-99/52867, the use of a mixture of methylamines allows theproduction of N-Methyl Pyrrolidone, in absence of added water, still inhigh purity and yield. The unreacted di and trimethylamines (andmethanol) are recycled in the amination section.

The above feature gives way to the production of NMP at low investmentcosts, using cheaper raw materiali and inferior utility consumptions,compared with the technologies of the previous art.

DESCRIPTION OF THE INVENTION

As known in the art, ammonia and methanol, reacting over an animatorcatalyst, produce a mixture of mono, di and trimethylamines (MMA, DMA,TMA).

The separation or the methylamines involves a complex sequence of 4 to 5fractionators requiring significant investment and high energyconsumptions.

The design of a methylamine plant can be driven toward the production ofone methylamine only by recycling to the amination reactor the remainingunwanted methylamines.

This practice, however, requires additional investments and more heavyenergy consumptions. Due to the above contraints a producer of NMP usingGBL and MMA as feedstocks would produce MMA only in case he caneconomically dispose the coproducts DMA and TMA.

The major innovation of the process of this invention is the possibilityof using mixtures of methylamines in place of MMA in the production ofNMP, making possible to establish a direct link between a NMP plant anda methylamines plant of cheaper design.

The synthesis of NMP from GBL and mixed amines follows basically thesame principles of the synthesis from GBL and MMA.

While one mole of GBL reacting with one mole of MMA forms one mole ofNMP and one mole of water, the reaction of one mole of GBL with one moleof DMA or with one mole of TMA forms, besides one mole of NMP,respectively one or two moles of methanol.

Consequently the product of the reaction will contain, besides NMP, nonconverted amines, water, methanol plus light and heavy by products.

Methanol and non converted amines, separated from the effluent ofreaction, will be recycled to the amination reactor where, in presenceof ammonia and of additional methanol, will be converted into mixedmethylamines.

The production of NMP from GBL and mixed methylamines in the process ofthis invention is characterized in that the synthesis is carried out bya continuous non catalytic process in the liquid phase, via distinctreaction stages, preferably, but not limited to, three connected inseries.

According to the present invention three stages of the reaction leadingto the production of NMP are characterised by what follows:

I stage of reaction Amines: GBL molar ratio = between 1.05 and 1.5Temperature (reactor outlet) = between 150 and 220° C. Residence time =between 10 and 40 minutes II stage of reaction Temperature = between 220and 270° C. Residence time = between 1 and 3 hours III stage of reactionTemperature = between 250 and 310° C. Residence time = between 0.5 and2.0 hours

In the three reactors the pressure ranges between 40 and 100.10 ⁵ Pa, soas to keep the reactants in their liquid phase.

All reactors are of the adiabatic type and preferably tubular in shape.

Adequate reactors are also vessels subdivided into compartments by meansof separation septs that avoid the reaction products to mix again as thereaction progresses.

In the first reactor GBL exothermally reacts with the amines to affordProduction of hydroxybutyramide (NMH). In the following reactor NMHcyclisation reaction is triggered with formation of water, methanol andNMP.

In the final stage, the NMP formation reaction goes to completion athigh temperature.

The succession of the subsequent reaction stages as they are describedin the present process leads to a reduction in GBL and NMH contents inthe reaction effluents, which is a necessary condition for producinghigh purity NMP (99.5% minimum weight).

GBL, whose boiling point is very close to that of MMP (202° C.) wouldnot be separated from NMP by distillation.

During distillation, NMH would tend to go off again yielding MMA and GBLthat would contaminate the product because not separable.

DESCRIPTION OF THE PROCESS

The features of the process of this invention will be more readilyapparent from the following description of the preferred embodiments ofthe invention with reference to the accompanying drawings in which theprocess schemes are shown. In the drawings

FIG. 1 shows a schematic representation of a process object of thisinvention for producing NMP from GBL and mixed methylamines.

FIG. 2 shows a schematic representation of a process for producing mixedmethylamines integrated with the NMP process object of this invention.

With reference to FIG. 1, mixed amines (line 1) mix with water (line 2)and with GBL (line 3) in static mixer 4 with a molar ratio of about1.2:1 between methylamines and GBL.

The mixing activates the addition reaction with formation of NMH.

This reaction is exothermal and once gone to completion takes the masstemperature up to about 190° C.

The addition reactions go to completion in reactor 5 within about 20minutes.

The liquid stream from the reactor (line 6) is heated up further inexchanger 7, by means of hot oil, and its temperature is taken up to250° C.

After preheating, the liquid (line 8) feeds reactors 9 where NMH startsto cyclise, while water and methanol are formed at the same time.

Residence time in reactor 9 is approximately 2 hrs. The reactor is ofthe tubular type, otherwise it is a vessel subdivided into compartmentsby separation septs that have the function of keeping the reactionproducts from mixing again.

The effluents from reactor 9 (line 10) feed heater 11 where temperatureis raised to 280° C. by thermal exchange with hot oil.

After the second preheating, the liquid (line 12) feeds reactor 13 whereconversion of NMH to NMP goes to completion with an approx. 1.5 hr. ofresidence time. Through valve 15, the effluent pressure is reducedproducing a liquid phase in separator 16 (line 17), and a vapour phase(line 18) which both feed fractionation column 19 where non convertedmethylamines and methanol separate overheads and are recycled to theamination reactor in the methylamine plant (line 100).

The bottom product of column 19 feeds (line 20) subsequent column 21,wherein at the top reaction water separates (line 22) while lightorganic byproducts are obtained too (line 23).

The bottom product in column 21 feeds (line 24) fractionation column 25where at the bottom heavy by-products are disposed (line 26) whereas atthe top (line 27) purified NMP separates.

After GC analysis NMP results to be no less pure than 99.5% by weight,with a water content lower than 0.05% by weight.

FIG. 2 shows a schematic representation of a process for producing mixedmethylamines integrated with the NMP process object of this invention.

Non converted amines and methanol stream from the NMP plant (line 100)join make up ammonia (line 101), make up methanol (line 102) and arecycling ammonia rich stream (line 116).

The mixture (line 104) after preheating (105) flows (line 106) to theamination reactor 107.

The reactor effluent (line 108) preheats the reactor feed in 105 and,following the preheater, (line 109) is condensed in cooler 110.

The condensate flows (line 111) to separator 112, where gases containingcarbon monoxide and hydrogen are separated (line 113). The condensateflows (line 114) to column 115 which separates overheads (line 116) anammonia-trimethylamine stream, which is recycled (line 116). Bottoms ofcolumn 115 flow (line 117) to column 118 which separates at bottomswater to be disposed (line 119) and overheads a stream of mixedmethylamines which flows to the NMP plant (line 1).

1. A process for the production of N-methyl-pyrrolidone, whichcomprises: reacting gamma butyrolactone and mixed methylaminesconsisting of a mixture of mono, di and trimethylamine or anycombination of the abovementioned methylamines wherein the reactingoccurs in a continuous non catalytic manner in the liquid phase, viastages of reaction connected in series; and recycling effluent obtainedfrom said reacting to an amination reactor; wherein said effluentcomprises unreacted mixed methylamines and methanol; and then contactingthe effluent comprising unreacted mixed methylamines and methanol withammonia and with externally added methanol to obtain a mixturecomprising mixed methylamines.
 2. A process according to claim 1,wherein there are three stages of the reaction having the followingcharacteristics: a) the first stage of the reaction operates at atemperature ranging between 150° C. and 220° C. at the reactor outlet,with a residence time ranging between 10 and 40 minutes; b) the secondstage of the reaction operates at a temperature ranging between 220° C.and 270° C. at the reactor inlet, with a residence time ranging between1 and 3 hrs; c) the third stage of the reaction operates at atemperature ranging between 250° C. and 310° C. at the reactor inlet,with a residence time ranging between 0.5 and 2 hrs.
 3. A processaccording to claim 1, wherein a first stage of the reaction operates ata temperature ranging between 170° C. and 200° C. at the reactor outlet.4. A process according to claim 1, wherein a first stage of the reactionhas a residence time that ranges from 15 to 25 minutes.
 5. A processaccording to claim 1, wherein a second stage of the reaction has aresidence time that ranges from 1.5 to 2.5 hrs.
 6. A process accordingto claim 1, wherein a third stage of the reaction has a residence timethat ranges from 1.0 to 1.5 hours.
 7. A process according to claim 1,wherein said reacting the molar ratio between mixed methylamines andgammabutyrolactone ranges from 1.05 to 1.5.
 8. A process according toclaim 1, wherein said reacting the molar ratio between mixedmethylamines and gammabutyrolactone ranges from 1.1 to 1.3.
 9. A processaccording to claim 1, wherein said reacting the reactants are kept inthe liquid phase by operating the reaction system at pressure thatranges from 40 to 100 ATE.
 10. A process according to claim 1, whereinsaid reacting occurs at pressure that ranges from 60 to 80 ATE.
 11. Aprocess according to claim 1, wherein reactors of each of the reactionstages consist of vessels having septs with the function of creating apiston-reactant-flow through separate reaction compartments which keepthe products from remixing.
 12. A process according to claim 11 whereinthe reactors of each of the reaction stages consist of vesselscharacterized by being tubular.
 13. A process for the production ofN-methyl-pyrrolidone according to claim 1, wherein said recycling isintegrated with said reacting.